Cargo hoist system for helicopters

ABSTRACT

A cargo hoist system for a helicopter including a boom extensible along its length, operatively connected at one end thereof to the helicopter, carrier means detachably connectable to a cargo unit to be hoisted, means disposed on the free end of the boom detachably connectable to the carrier means, and means for retracting the extensible boom.

United States Patent lnventor Frank N. Piasecki Haveriord, Pa. Appl. No. 835,049 Filed June 20, 1969 Patented Aug. 24, 1971 Assignee Piasecki Aircraft Corporation Philadelphia, Pa.

CARGO HOIST SYSTEM FOR HELICOPTERS 35 Claims, 1 1 Drawing Figs.

U.S.Cl 244/137, 52/118, 52/121, 212/55, 254/143 Int. Cl 864d 9/00 Field of Search 244/137; 212/55;254/143;52/118, 121

Relerencs Cited UNITED STATES PATENTS 2,585,030 2/1952 Nosker 244/137 X 3,109,545 11/1963 Hedin 212/55 X 3,227,401 1/1966 Currier 244/137 3,329,291 7/1967 Przybylski et al.... 212/55 3,331,572 7/1967 Guin 244/137 3,358,950 12/1967 Welsch et al. 244/137 3,450,376 6/1969 Rusanovich et a1 244/137 Primary Examiner-Milton Buchler Assistant ExaminerSteven W. Weinrieb Attorney-Mason, Fenwick & Lawrence ABSTRACT: A cargo hoist system for a helicopter including a boom extensible along its length, operatively connected at one end thereof to the helicopter, carrier means detachably connectable to a cargo unit to be hoisted, means disposed on the free end of the boom detachably connectable to the carrier means, and means for retracting the extensible boom.

PATENTEUAUGZMSYI 3 501 342 SHEET 1 0F 5 INVENTOR FRANK N. Dmsacm ATTORNEYS PATENTED AUG24 l97| SHEEI 2 OF 5 (4 ATTORNEYS SHEET 3 OF 5 PATENTED M1824 1971 FRANK N 'Pmvsecxm BY mwsm 'wuwk ig c.

' ATTORNEYS PmgminAus24197| 3.601.342

- SHEEI [1F 5 INVENTOR FRANK N. Pmsacm i. ATTORNEYS PATENTEUAus24|97| 3.601.342

' SHEET 5 UF 5 INVENTOR FRANK N- D\A$EKJ\ ATTORNEYS CARGOI-IOIST SYSTEM lFOli ii'ntlcormns This invention relates to a hoist system and more particularly to a cargo hoist system for helicopters.

The advent of heavy lift helicopters for transporting cargo in military and commercial applications has necessitated the development of a cargo hoist system having the capability of lifting and lowering various types of bulky loads. It particularly has become desirable to provide a cargo hoist system which is effective in rapidly and reliably attaching, lifting and lowering, and detaching the cargo, while being compatible with the helicopter in flight.

Various types of hoist system for helicopters have been developed in the prior art. However, it has been found that such systems are not entirely satisfactory in performance. Many conventional-type systems have been found to be undesirable in that they often have excessive component weights, incompatible configurations, poor reliability and maintainability, inadequate in flight safety capabilities and complex controls.

Accordingly, it is the principal object of the present invention to provide a novel cargo hoist system.

Another object of the present invention is to provide a novel cargo hoist system adapted for use with helicopters.

A further object of the present invention is to provide a novel cargo hoist system adapted for use with helicopters either while landed or hovering.

A still further object of the present invention is to provide a novel cargo hoist system adapted for use with helicopters and which is adapted to lift and lower bulky loads.

Another object of the present invention is to provide a novel cargo hoist system for a helicopter having a minimum weight.

A further object of the invention is to provide an improved cargo hoist system for a helicopter which is reliable in performance, and which requires minimum maintenance.

A still further object of the present invention is to provide an improved cargo hoist system for a helicopter which provides maximum in-flight safety.

A more specific object of the present invention is to provide a novel cargo hoist system for a helicopter which permits acceptable freedom of movement of the cargo in pitch and roll, and which further provides yaw stabilization.

Another object of the present invention is to provide a novel cargo hoist system for a helicopter which is effective in minimizing unsafe oscillations of a suspended load.

A further object of the invention is to provide a novel cargo hoisting system for a helicopter which is capable of rapid load acquisition and removal with manual ground assistance while the helicopter is hovering or landed.

A still further object of the present invention is to provide a novel cargo-handling system for a helicopter wherein the major components thereof may be quickly detached and removed from the helicopter so that the helicopter can function in other modes of operation.

Another object of the present invention is to provide a novel hoist assembly for a cargo-hoisting system.

A further object of the present invention is to provide a novel pallet adapted for use in a cargo hoist system.

A still further object of the present invention is to provide a novel cargo hoist system for a helicopter which is comparatively simple in construction, relatively inexpensive to manufacture, and simple to operate.

Other objects and advantages of the present invention will become more apparent to those persons having ordinary skill in the art to which the invention pertains, from the following description taken in conjunction with the accompanying drawings, wherein:

FIG. 1 illustrates an embodiment of the invention shown in different sequences of operation;

FIG. 2 is a perspective view of a pallet which constitutes a part of the embodiment illustrated in FIG. ll;

FIG. 3 is an enlarged end view of the pallet illustrated in FIG. 2, having portions thereof broken away;

FIG. 4 is an enlarged cross-sectional view taken along line 4-4 in FIG. 3;

FIG. 5 is a front view of a modified pickup ball or hoop assembly adapted for use in the pallet illustrated in FIG. 2;

FIG. 6 is an enlarged cross-sectional view taken along line 6-6 in FIG. 5;

FIG. 7 is an enlarged front view of the upper end of the assembly illustrated in FIG. 5;

FIG. 8 is an enlarged perspective view of the hoist assembly of the embodiment illustrated in FIG. 1, having a portion thereof broken away;

FIG. 9 is an enlarged cross-sectional view taken along line 9-'-9 in FIG. 8;

FIG. 10 is a perspective view of a part of the lifting strap illustrated in FIG. 8, and

FIG. 11 is a perspective view of a modification of the hoist assembly illustrated in FIG. 8, having a portion thereof broken away.

Briefly described, the present invention relates to a cargo hoist system for a helicopter generally including a boom extensible along its length, operatively connected at one end thereof to. the helicopter, carrier means detachably connected to the cargo to be hoisted, means disposed on the free end of the boom detachably connectable to the carrier means, and means for retracting the extension boom.

Preferably, the extensible boom comprises a plurality of telescopic sections each having a noncircular cross-sectional configuration and means disposed at the opposite ends thereof for limiting the longitudinal displacement thereof relative to successive telescopic sections. The connection of the extensible boom to the helicopter is operative to permit pitch and roll motions of the extensible boom, and the carrier means includes a rigid ball or hoop. In addition, it is preferred that the means disposed on the free end of the extensible boom comprises a hook device mounted on a telescopic boom section, operatively engageable with the hoop of the carrier means for engaging and suspending the carrier means on the free end of the extensible boom, and the means for retracting the extensible boom comprises a winch disposed adjacent the helicopter, including a multiple-ply strap having the free end thereof secured to the telescopic boom section at the free end of the extensible boom.

Referring to FIGS. 1 through 4, and 8 through 9 of the drawings, there is illustrated an embodiment of the invention. The embodiment consists of a cargo hoist system for a helicopter, including a hoist assembly 10 connected to the fuselage of a helicopter 11, and a pallet 12 on which a cargo unit 13 may be secured, and whichis adapted to be detachably connected to the hoist assembly. As best illustrated in FIG. 8, the boom assembly 10 includes an extensible boom 14, a connecting assembly 15 for connecting the upper end of the extensible boom to the helicopter 11, a hook device 16 disposed on the free end of the extensible boom, a winch assembly 17 for retracting the extensible boom, and an actuating unit 18 for pivoting the extensible boom in its extended position, substantially fore and aft about the pitch axis of the boom.

The extensible boom 14 consists of a plurality of telescopic sections 19, each having a rectangular cross-sectional configuration. As best illustrated in FIG. 9, each section I9 is provided with an outwardly projecting peripheral flange 20 and an inwardly projecting peripheral flange 21 at the upper end thereof, and an inwardly projecting peripheral flange 22 at the lower end thereof. The outwardly projecting flange 20 of each section 19 is engageable with the inwardly projecting flanges 21 and 22 of a successive section 19 to limit the displacement of each section 19 relative to a successive similar section. It will be appreciated that when the extensible boom is in its maximum extended position, each section will be supported upon an upper successive section by means of the flange 20 thereof engaging and resting on the flange 22 of the upper successive section. Also, when the extensible boom is in its maximum retractedposition, the outwardly projecting flange 20 of a section 19 will engage the inwardly projecting flange 21 of an upper successive section to limit the upward travel of each section 19 and position the plurality of sections in nested relation.

The lowermost telescopic section 19a is formed integral with a shank portion 16a of the hook device 16. The device 16 may be of any suitable construction which is cooperable with the pallet 12 to rapidly attach or detach the pallet 12 on or off the free end of the extensible boom 14. Preferably, the hook device is of the type as disclosed in US. Pat. No. 3,039,746, issued June 19, 1962. The uppermost telescopic section 1912 is provided with a pair of upstanding brackets 23 and 24 for pivotally connecting the upper end of the extensible boom to the connecting assembly 15.

The connecting assembly includes a base member 25 rigidly mounted to the fuselage of the helicopter 11, and a mounting frame 26 interconnecting the base member 25 and the upper end of the extensible boom 14 and supporting the winch assembly 17. The base member 25 is provided with a pair of depending brackets 27 and 28 having a longitudinally disposed pivot pin 29 on which the upper end of the mounting frame 26 is pivotally connected. The mounting frame 26 includes a base section 30 pivotally mounted on pivot pin 29, and a pair of transversely spaced depending arms 31 and 32. The lower ends of the arm members 31 and 32 are provided with aligned, transversely disposed pivot pins 33 and 34 which pivotally interconnect the lower ends of depending arms 31 and 32 on the mounting frame and the upper ends of brackets 23 and 24 of telescopic section 19b. It will be appreciated that the pivotal connection between the mounting frame 26 and the base member 25, and the pivotal connection between the telescopic section 19b and the mounting frame 26 permits the extensible boom to freely roll and pitch. The connecting assembly 15 may be provided with suitable devices for damping any oscillating motion of the extensible boom about its roll and pitch axes.

The movement of the extensible boom in substantially a fore-and-aft direction is controlled by the actuating unit 18 consisting of a fluid cylinder assembly operatively interconnecting the fuselage of the helicopter and the upper end of the extensible boom. As illustrated in FIG. 8, the fluid cylinder assembly is provided with a cylinder 35 having the forward end thereof pivotally connected to a bracket 36 rigidly mounted on the fuselage of the helicopter, and a piston 37 having the rear end thereof pivotally connected to a bracket 38 rigidly mounted on the uppermost telescopic section 19b. The actuating unit 18 is positioned to move the boom to the right as well as forward, for a purpose hereinafter explained.

The winch assembly 17 consists ofa winding drum 39, a lifting strap 40, a gear reduction unit 41, and a fluid motor 42. The winding drum 39 is disposed within the mounting frame 26 and is rotatably supported on a shaft 43 mounted in the depending arms 31 and 32. The lifting strap 40 extends through the interior of the extensible boom 19, having the lower end thereof secured to the lowermost telescopic section 19a and the upper end thereof operatively connected to the winding drum 39 to permit the strap to be wound on the winding drum as the drum is rotated. The drum is driven by means of the fluid motor 42 mounted on the mounting frame 26. Drive is transmitted from the fluid motor 42, through the gear reduction unit 41, to a pair of gears 43 and 44 mounted on the ends of the drum. The fluid motor 42 also is provided with suitable fluid supply lines 45 and 46 connected to a source of fluid under pressure on the helicopter, and is controlled by a suitable control system aboard the helicopter.

Although the cross-sectional configuration of each of the telescopic sections 19 is illustrated as rectangular in the drawings, it is to be understood that any configuration which will prevent rotary displacement between successive telescopic sections may be employed. Practically any noncircular cross-sectional configuration can be employed, although it is preferred that the configuration be streamlined so as not to appreciably affect the operation of the helicopter in flight. The telescopic sections 19 can also be constructed of any lightweight material having sufficient strength characteristics,

and being capable of assuming the torsional load applied on the boom by the cargo carried by the boom. It further is contemplated that the telescopic boom sections may be constructed of a low-density fiber glass material.

As illustrated in FIG. 10, the lifting strap 40 consists of a plurality of plies 40a, preferably secured together by a resilient bonding material 40b. This construction of the lifting strap provides sufficient strength to permit lifting of heavy loads and facilitates the winding and unwinding of the strap on the drum 39. The multiple-ply construction provides a small bending radius and will wrap upon itself while under load without any wear results or fatigue. Normal wear of the lifting strap in a torsional direction is eliminated as a result of the torsional load on the system being taken by the telescopic sections of the boom.

An appropriate control system is provided in the helicopter for the winch assembly 17 and the actuating unit 18 to lift and lower the extensible boom, and to pitch it forward and aft. In addition, the control system is adapted to control the hook device 16 to pick up and release the pallet 12.

Referring to FIG. 2, the pallet 12 includes an elongated frame assembly 47 and a bail or hoop assembly 48. The frame assembly consists of a pair of triangularly arranged end members 49 and 50 having the upper apices thereof interconnected by extruded beam 51 and corresponding lower apices interconnected by extruded beams 52 and 53. The frame further is provided with a plurality of cross braces 54. The beam 51 is provided on its upper end with a T-shaped groove 55 which extends the entire length of the beam. The lower beam 52 is provided with T-shaped slots 56 and 57 along the side and bottom portions thereof, which are similar in cross-sectional configuration to the slot 55. Similarly, the beam 53 is provided with T-shaped slots 58 and 59 on the side and bottom portions thereof. The bail unit 48 is provided with a transverse beam 60 having a pair of upstanding brackets 61 and 62 mounted on the ends thereof. The lower ends of an inverted V-shaped hoop 63 are pivotally connected on the upper ends of the brackets 61 and 62, by means of a pair of pivot bolts 64 and 65, so that the hoop can be positioned in the vertical position as illustrated by the solid lines in FIG. 2, or pivoted downwardly to a stowage position, as illustrated by the phantom lines.

The transverse beam 60 is secured to the beam 51 of the frame assembly by means of a bolt 66 extending through vertically aligned openings in the transverse beam and threaded into a threaded opening in a slide key 67 disposed in slot 55, as best illustrated in FIG. 4. It will be seen that the transverse beam 60 may be positioned anywhere along the beam 51 by loosening the bolt 66, sliding the transverse beam to the desired location along the beam 51, and tightening the bolt 66. The transverse beam 60 further is rigidly secured to the frame assembly by means of pairs of straps 68a and 69a. The pairs of straps are provided with fittings 70 and 71 and have the upper ends thereof secured to lugs depending from the end portions of the transverse beam 60. The lower ends of the straps are connected to slide keys 68b and 69b which are mounted in slots 57 and 59. The strap fittings are used to draw the straps 68a and 69 a taut to firmly secure the transverse beam 60 in position on the frame assembly. The hoop 63 further is provided with a pin 72 secured to a chain, which is adapted to be inserted through registerable openings in the end portion 63a ofthe hoop and the bracket 62 when the hoop is in the upright position to lock the hoop in such position. The frame assembly further is provided with a plurality of straps 73 which are adapted to pass under the cargo unit and be connected together to firmly secure the cargo to the underside of the frame assembly. The upper ends of the securing straps are connected to slide keys 74 which are disposed in the slots 56 and 58. The slide elements 74 may be positioned anywhere along the slots 56 and 58 to accommodate cargo units of different lengths. The frame assembly also is provided with a plurality of cushion pads 680 which are slidably mounted in key slots 57 and 59, and which are adapted to be positioned along the lengths thereof to engage the cargo unit when the cargo unit is secured to the pallet.

In the use of the cargo hoist system as described, the cargo unit 13 is secured to the pallet 12, as illustrated in FIG. 1. This may be accomplished by first positioning the hoop assembly 48 on the frame assembly 47, securing the hoop assembly in position by tightening the bolt 66 and adjusting the fittings 70 and 71, placing the hoop 63 in the upright position, and locking the hoop in position by means of the locking pin 72. The pallet is then placed on the cargo unit 13 so that the cushion pads engage and rest on the cargo unit. The securing straps 73 are then passed under the cargo unit and connected together to firmly secure the cargo unit to the frame assembly 47. It will be noted that the hoop assembly 48, the securing straps 73, and the cushion pads 74 may be positioned along the length of the frame assembly in accordance with the length of the cargo unit. The pallet and cargo unit then are ready to be picked up by the hoist assembly on the helicopter.

To pick up the pallet and attached cargo unit, the pilot of the helicopter operates the winch assembly to extend the boom to its maximum extended position. The hook device 16 of the boom is then positioned near ground level on the right side of the helicopter at a lateral distance approximately equal to the main landing gear width, and forwardly atapproximately the front end of the helicopter nose, as illustrated in the first sequence in FIG. 1. The fluid pressure in cylinder 35 is sufficient to position the boom in this manner only when it has no cargo attached. The pilot maneuvers the helicopter so that the hook device is positioned at the left rear end of the cargo unit and then maneuvers slowly forwardly and laterally to place the hook through the loop of the pallet. After the hook is through the loop, the helicopters collective pitch is raised slightly and the hook automatically engages the loop and locks. The pilot then continues to raise the helicopter with a slight forward motion, thus allowing the boom holding the pallet to lower automatically below the center of gravity of the helicopter. This motion iscontinued until the cargo unit is off the ground and forward translation is accelerated.

When the cargo unit is positioned below the center of gravity of the helicopter, as illustrated in the second sequence in FIG. 1, the winch assembly is operated to lift the cargo unit adjacent the fuselage of the helicopter, as illustrated in the third sequence in FIG. 1. The helicopter and the cargo load are then in condition for normal flight operations. When it is desired to unload the cargo unit, the pilot may either land the helicopter and remove the cargo unit, or maneuver the helicopter to a position approximately 150 feet off the ground and hover whileoperating the winch to extend the boom. As soon as the cargo unit is positioned on the ground, the pilot may disengage the hook device and resume his flight operations. In doing so, the winch assembly is operated to retract the boom. Ground personnel also may then quickly remove the cargo unit from the pallet and stow the pallet for future use.

It thus will be appreciated that once the cargo unit is secured to the pallet, the helicopter pilot may easily and rapidly pick up the cargo unit, transport it to another location, and easily and rapidly deposit it on the ground.

It is contemplated that the boom 14 have a length of approximately 150 feet when extended to its maximum extended length. It further is contemplated that because of the telescopic construction of the boom, it can be readily retracted to a length as little as 2 feet. As previously mentioned, both the pitch and roll motions can be dampened about the booms pivotal connections with the helicopter with hydraulic dampeners. Wear on the lifting strap by winding and unwinding forces in a torsional direction are eliminated by the torsional load being applied to the boom in lieu of the lifting strap. In order to maintain a minimum slack in the lifting strap, a constant tension clutch can be used on the winding drum of the winch assembly.

FIGS. 5 through 7 illustrate a modification of the pallet 12. The modification includes a frame assembly 75 which is essentially similar to the frame assembly 47, and a hoop assembly 76. The hoop assembly includes a mounting bracket 77 having a pair of spaced upright sections 78 and 79, secured to a longitudinal beam 80 of the frame assembly, a connecting member 81 pivotally connected to the bracket 77, a pair of lower rigid hoop sections 82 and 83, and a pair of upper rigid hoop sections 84 and 85. The connecting member 81 is provided with a pair of upright portions 86 and 87, in which a pair of pivot bolts 88 and 89 are secured, and a depending arm portion 90 which is pivotally mounted on a pivot pin 91 mounted in the upright sections 78 and 79 of the bracket 77. The depending arm portion 90 of the connecting member and the upright sections 78 and 79 are provided with openings which are registerable when the hoop assembly is disposed vertically, for receiving a locking pin 91a therethrough, as best illustrated in FIG. 5.

The lower ends of the hoop sections 82 and 83 are pivotally mounted on pivot pins 88 and 89 to permit pivotal movement thereof in a vertical plane. The lower ends of the hoop sections 82 and 83 are provided with stop elements 92 and 93 which are adapted to engage the connecting member 81 to limit the lateral movement of the lower hoop sections, thus preventing the hoop assembly from totally collapsing. The lower ends of the upper hoop sections 84 and 85 are pivotally connected to the upper ends of the hoop sections 82 and 83,

and are pivotally connected together at their upper ends. As best illustrated in FIGS. 5 and 7, the upper ends of the hoop sections 84 and 85 are curved inwardly as at 84a and 85a, so that when a hook 16a of the hook-on device engages the underside of either hoop section 84 or hoop section 85, and moved upwardly to cause the upper hoop members to move inwardly as illustrated by the phantom lines in FIG. 5, the upper end of the hoop assembly will provide a curved engaging portion for thehook, thus preventing any binding action between the hook and the upper end of the hoop assembly.

The pallet illustrated in FIGS. 5 through 7 is utilized essentially in the same manner as the pallet illustrated in FIGS. 2 through 4. However, when the pallet is being prepared for a pickup operation, it is necessary for ground personnel to lock the hoop assembly in the vertical position by means of the locking pin 91, and spread the lower hoop sections 82 and 83 so that the stop elements 92 and 93 engage the connecting member 81, thus providing a sufficiently large opening in the assembly to facilitate the insertion of the hook therewith.

FIG. 11 illustrates another embodiment of the hoist assembly which consists of an extensible boom 94, an assembly 95 for connecting the upper end of the extensible boom to the fuselage of the helicopter, a hook-on device 96 mounted on the free end of the extensible boom, and a winch assembly 97. The extensible boom 94 comprises a plurality of telescopic sections 98 which are similar to the telescopic boom sections 19 of the extensible boom 14 illustrated in FIG. 8, except that the telescopic sections 98 are provided with a streamlined cross-sectional configuration. The uppermost telescopic section 980 is mounted on an upper mounting frame 99 which is connected by means of a linking member 100 to a mounting bracket similar to bracket 25 of hoist assembly 14 illustrated in FIG. 8. The upper frame unit 99 includes a pair of laterally spaced sidewalls 101 and 102 which are provided with a pair of upright brackets 101a and 102a. The upper ends of brackets 101a and 102a are pivotally connected to the linking member 100 by means of a transverse pivot pin 103, while the upper end of the linking member 100 is provided with an opening for receiving a longitudinal pivot pin similar to the pivot pin 29 of the hoist assembly 14 illustrated in FIG. 8. Such pivotal connections permit the extensible boom 94 to roll and pitch similar to the hoist assembly 14.

The winch assembly 97 consists of a winding drum 104 journaled in side members 101 and 102 of the upper mounting frame, a first set of sheaves 105 and 106 also journaled in the side members 101 and 102 of the upper mounting frame, a second set of sheaves 107 and 108 journaled in a lower mounting frame 109 secured to the lowermost telescopic section 98b, and a lifting strap 1 10 having one end thereof operatively connected to the winding drum 104, the intermediate portion thereof reeved under sheave 107, over sheave 105, under sheave 108 and over sheave 106, and the other end thereof secured to the lower mounting frame 109. The winding drum 104 further is provided with a fluid motor 111 which is remotely operated to drive the winding drum 104 through a gear reduction train 112. It will be appreciated than upon operation of the fluid motor 97 to drive the winding drum 104, the lifting strap 1 10 will be taken in or played out to extend or retract the extensible boom. In other respects, the extensible boom 94 is similar in construction and operation to the extensible boom 14, as illustrated in FIG. 8. The hook-on device 96 also may be similar to the hook-on device 16 of the extensible boom 14.

I claim:

1. A cargo hoist system for a helicopter comprising a single boom extensible along its length, operatively connected at one end thereof to said helicopter, carrier means detachably connectable to cargo to be hoisted, means disposed on the free end of said boom detachably connectable to said carrier means, and means disposed on said helicopter and extending entirely within said boom for retracting said extensible boom along its length.

2. A cargo hoist system for a helicopter according to claim 1, wherein said extensible boom comprises a plurality of telescopic sections.

3. A cargo hoist system for a helicopter according to claim 1, wherein said extensible boom comprises a plurality of telescopic sections and wherein successive sections are provided with engageable surfaces for preventing rotary displacement of successive sections about the longitudinal axis of said extensible boom.

4. A cargo hoist system for a helicopter according to claim 1, wherein said extensible boom comprises a plurality of telescopic sections each having a noncircular cross-sectional configuration and means disposed at the opposite ends thereof for limiting the longitudinal displacement thereof relative to a successive telescopic section.

5. A cargo hoist system for a helicopter according to claim 1, wherein the connection of said extensible boom to said helicopter is operative to permit pitch and roll motions of said extensible boom.

6. A cargo hoist system for a helicopter according to claim 1, wherein said carrier means includes a collapsible hoop and said means disposed on the free end of said extensible boom comprises a hook device operatively engageable with said hoop for engaging and suspending said carrier means on the free end ofsaid extensible boom.

7. A cargo hoist system for a helicopter according to claim 1, wherein said means for retracting said extensible boom comprises a winch including a cable having the free end thereof secured to the free end of said extensible boom.

8. A cargo hoist system for a helicopter according to claim 1, including means for pivoting said boom in the extended condition about a pitch axis.

9. A cargo hoist system for a helicopter according to claim 1, wherein said means for retracting said extensible boom comprises a winch including a strap having the free end thereof secured to said means detachably connectable to said carrier means.

10. A cargo hoist system for a helicopter according to claim 1, wherein said extensible boom comprises a plurality of telescopic sections each having a noncircular cross-sectional configuration and means disposed at the opposite ends thereof for limiting the longitudinal displacement thereof relative to a successive telescopic section and wherein said means for retracting said extensible boom comprises a winch disposed adjacent said helicopter including a multiple-ply lifting strap having the free end thereof secured to said means detachably connectable to said carrier means.

11. A cargo hoist system for a helicopter according to claim 1, wherein said extensible boom comprises a plurality of telescopic sections each having a noncircular cross-sectional configuration and means disposed at the opposite ends thereof for limiting the longitudinal displacement thereof relative to a successive telescopic section, said connection of said extensible boom to said helicopter is operative to permit pitch and roll motions of said extensible boom, said carrier means includes a hoop, said means disposed on the free end of said extensible boom comprises a hook device mounted on a telescopic boom section, operatively engageable with said hoop for engaging and suspending said carrier means on the free end of said extensible boom, and said means for retracting said extensible boom comprises a winch disposed adjacent said helicopter including a multiple-ply lifting strap having the free end thereof secured to the telescopic boom section at the free end of said extensible boom, and including means for pivoting said extensible boom in the extended condition about its pitch axis.

12. A cargo hoist system for a helicopter according to claim 1, wherein said means for retracting said extensible boom comprises a winch including a winding drum disposed adjacent the helicopter and a cable reeved about a first set of sheaves mounted on the free end of said extensible boom and a second set of sheaves mounted adjacent said drum, and the free end thereof secured to the free end of said extensible boom.

13. A cargo hoist system according to claim 1, wherein said carrier means detachably connectable to cargo to be hoisted, comprises an elongated frame adapted to be positioned on the cargo to be hoisted, a hoop adapted to be engaged and connected by said detachably connectable means disposed on the free end ofsaid boom, and means for detachably securing said cargo to the underside of said frame.

14. A cargo hoist system for a helicopter according to claim 13, wherein said means for securing said cargo to the underside of said elongated frame comprises a plurality of straps adapted to be passed under the cargo and drawn taut to positively secure the cargo to the underside of said elongated frame.

15. A cargo hoist system for a helicopter according to claim 1, wherein said extensible boom comprises a plurality of telescopic sections each having a noncircular cross-sectional configuration and means disposed at the opposite ends thereof for limiting the longitudinal displacement thereof relative to a successive telescopic section, and wherein said connection of said extensible boom to said helicopter includes a mounting bracket mounted on said helicopter, a mounting frame pivotally connected to said mounting bracket and a base end telescopic section pivotally connected to said mounting frame.

16. A cargo hoist system for a helicopter according to claim 13, wherein said pivotal connection between said mounting frame and said mounting bracket permits pivotal movement of said boom about a roll axis and said pivotal connection between the base and telescopic section of said boom and said mounting frame permits pivotal movement of said boom about a pitch axis.

17. A cargo hoist system according to claim 16, including means for dampening any oscillating motion of said extensible boom about at least one of said axes.

18. A cargo hoist system for a helicopter according to claim 15, wherein said means for retracting said extensible boom comprises a winch including a winding drum operatively mounted on said mounting frame and a cable extending through said telescopic boom sections and connected at its free end to the telescopic boom section at the free end of said boom, and means mounted on said mounting frame for operating said winch.

19. A cargo hoist system according to claim 18, including a first set of sheaves mounted on said mounting frame and a second set of sheaves mounted on said telescopic boom section at the free end of said boom, and wherein said cable is reeved about said sheaves.

20. A cargo hoist system according to claim 15, including a hydraulic cylinder assembly operatively interconnecting said helicopter and a base end telescopic section for pivoting said boom fore and aft about a pitch axis, and remote control means for operating said hydraulic cylinder assembly.

21. A cargo hoist system for a helicopter according to claim 15, wherein said connection of said extensible boom to said helicopter permits pivotal movements of said boom about roll and pitch axes, and wherein said means for retracting said extensible boom comprises a winch including a winding drum rotatably mounted on said mounting frame, having an axis of rotation disposed parallel to said pitch axis, and a multiple ply lifting strap extending through said telescopic boom sections and connected at its free end to the telescopic boom sections at the free end of said boom, and means mounted on said mounting frame for operating said winch including remote control means,

22. A cargo hoist system according to claim 17, including a first set of sheaves rotatably mounted on said mounting frame, having axes disposed parallel to the axis of rotation of said winding drum, and a second set of sheaves rotatably mounted on said telescopic boom section at the free end of said boom, and wherein said strap is reeved about said sheaves.

23. A cargo hoist system according to claim 15, wherein said extensible boom comprises a plurality of telescopic sections each having a noncircular cross-sectional configuration and means disposed at the opposite ends thereof for limiting the longitudinal displacement thereof relative to a successive telescopic section, and wherein said connection of said extensible boom to said helicopter includes a bracket mounted on said helicopter, a mounting frame pivotally connected to said mounting bracket to permit movement of said extensible boom about a roll axis, said mounting frame having a pair of downwardly extending arm sections, a base end telescopic section pivotally connected to the arm sections of said mounting frame to permit pivotal movement of said extensible boom about a pitch axis, and wherein said means for retracting said extensible boom comprises a winch including a winding drum rotatably connected to said frame member between said arm sections, having an axis of rotation disposed parallel with said pitch axis, and a multiple-ply lifting strap extending through said telescopic boom sections and connected at its free end to the telescopic boom section at the free end of said boom, and means mounted on said mounting frame for operating said winch having remote control means.

24. A cargo hoist system according to claim 18, including a hydraulic cylinder assembly operatively interconnecting said helicopter and said base end telescopic section for pivoting said boom fore and aft about said pitch axis, and remote control means for operating said hydraulic cylinder assembly.

25. A cargo hoist system according to claim 23, including a first set of sheaves rotatably mounted on said mounting frame between said arm sections, having the axes thereof disposed parallel to the axis of rotation of said winding drum, and a second set of sheaves mounted on said telescopic boom section at the free end of said boom, having the axes thereof disposed parallel to the axis of rotation of said winding drum, and wherein said strap is reeved about said sheaves.

26. A cargo hoist system for a helicopter comprising a boom extensible along its length, operatively connected at one end thereof to said helicopter, carrier means detachably connectable to cargo to be hoisted, means disposed on the free end of said boom detachably connectable to said carrier means, and means for retracting said extensible boom, said extensible boom comprising a plurality of telescopic sections each having a noncircular cross-sectional disposed at the opposite ends thereof for limiting the longitudinal displacement thereof relative to a successive telescopic section and said means for retracting said extensible boom comprising a winch disposed adjacent said helicopter including a multiple-ply lifting strap having free end thereof secured to said means detachably connectable to said carrier means.

27. A cargo hoist system for a helicopter comprising a boom extensible along its length, operatively connected at one end thereof to said helicopter, carrier means detachably connectaconfiguration and means ble to cargo to be hoisted, means disposed on the free end of said boom detachably connectable to said carrier means, means for retracting said extensible boom, aid extensible boom comprising a plurality of telescopic sections each having a noncircular cross-sectional configuration and means disposed at the opposite ends thereof for limiting the longitudinal displacement thereof relative to a successive telescopic section, said connection of said extensible boom to said helicopter being operative to permit pitch and roll motions of said extensible boom, said carrier means including a hoop, said means disposed on the free end of said extensible boom comprising a hook device mounted on a telescopic boom sec tion, operatively engageable with said hoop for engaging and suspending said carrier means on the free end of said extensible boom, and said means for retracting said extensible boom comprising a winch disposed adjacent said helicopter including a multiple-ply lifting strap having the free end thereof secured to the telescopic boom section at the free end of said extensible boom, and means for pivoting said extensible boom in the extended condition about its pitch axis.

28. A cargo hoist system for a helicopter comprising a boom extensible along its length, operatively connected at one end thereof to said helicopter, carrier means detachably connectable to cargo to be hoisted, means disposed on the free end of said boom detachably connectable to said carrier means, and means for retracting said extensible boom, said means for retracting said extensible boom comprising a winch including a winding drum disposed adjacent the helicopter and a cable reeved about a first set of sheaves mounted on the free end of said extensible boom and a second set of sheaves mounted adjacent said drum, and the free end thereof secured to the free end of said extensible boom.

29. A cargo hoist system for a helicopter comprising a boom extensible along its length, operatively connected at one end thereof to said helicopter, carrier means detachably connectable to cargo to be hoisted, 'means disposed on the free end of said boom detachably connectable to said carrier means, and means for retracting said extensible boom, said extensible boom comprising a plurality of telescopic sections each having a noncircular cross-sectional configuration and means disposed at the opposite ends thereof for limiting the longitudinal displacement thereof relative. to a successive telescopic section, said connection of said extensible boom to said helicopter boom sections and connected at its free end to the telescopic boom section at the free end of said boom, and means mounted on said mounting frame for operating said winch including remote control means.

30. A cargo hoist system according to claim 29, including a first set of sheaves mounted on said mounting frame and a second set of sheaves mounted on said telescopic boom section at the free end of said boom, and wherein said cable is reeved about said sheaves.

31. A cargo hoist system for a helicopter comprising a boom extensible along its length, operatively connected at one end thereof to said helicopter, carrier means detachably connectable to cargo to be hoisted, means disposed on the free end of said boom detachably connectable to said carrier means, and means for retracting said extensible boom, said extensible boom comprising a plurality of telescopic sections each having a noncircular cross-sectional configuration and means disposed at the opposite ends thereof for limiting the longitudinal displacement thereof relative to a successive telescopic section, said connection of said extensible boom to said helicopter including a mounting bracket mounted on said helicopter, a mounting frame pivotally connected to said mounting bracket and a base end telescopic section pivotally connected to said mounting frame, said connection of said extensible boom to said helicopter permits pivotal movements of said boom about roll and pitch axes, and said means for retracting said extensible boom comprising a winch including a winding drum rotatably mounted on said mounting frame, having a axis of rotation disposed parallel to said pitch axis, and a multiple ply lifting strap extending through said telescopic boom sections and connected at its free end to the telescopic boom section at the free end of said boom, and means mounted on said mounting frame for operating said winch including remote control means.

32. A cargo hoist system according to claim 31, including a first set of sheaves rotatably mounted on said mounting frame, have axes disposed parallel to the axis of rotation of said winding drum, and a second set of sheaves rotatably mounted on said telescopic boom section at the free end of said boom, and wherein said strap is reeved about said sheaves.

33. A cargo hoist system for a helicopter comprising a boom extensible along its length, operatively connected at one end thereof to said helicopter, carrier means detachably connectable to cargo to be hoisted, means disposed on the free end of said boom detachably connectable to said carrier means, and means for retracting said extensible boom, said extensible boom comprising a plurality of telescopic sections each having a noncircular cross-sectional configuration and means disposed at the opposite ends thereof for limiting the longitudinal displacement thereof relative to a successive telescopic section, said connection of said extensible boom to said helicopter includes a mounting bracket mounted on said helicopter and a mounting frame pivotally connected to said mounting bracket, said mounting frame having a pair of downwardly extending arm sections, a base end telescopic section pivotally connected to the arm sections of said mounting frame to permit pivotal movement of said extensible boom about a pitch axis, and said means for retracting said extensible boom comprising a winch including a winding drum rotatably connected to said frame member between said arm sections, having an axis of rotation disposed parallel with said pitch axis, and a multiple-ply lifting strap extending through said telescopic boom sections and connected at its free end to the telescopic boom section at the free end of said boom, and means mounted on said mounting frame for operating said winch having remote control means.

34. A cargo hoist system according to claim 33, including a hydraulic cylinder assembly operatively interconnecting said helicopter and said base end telescopic section for pivoting said boom fore and aft said pitch axis, and remote control means for operating said hydraulic cylinder assembly.

35. A cargo hoist system according to claim 33, including a first set of sheaves rotatably mounted on said mounting frame between said arm sections, having the axes thereof disposed parallel to the axis of rotation of said winding drum, and a second set of sheaves mounted on said telescopic boom section at the free end of said boom, having the axes thereof disposed parallel to the axis of rotation of said winding drum, and wherein said strap is reeved about said sheaves. 

1. A cargo hoist system for a helicopter comprising a single boom extensible along its length, operatively connected at one end thereof to said helicopter, carrier means detachably connectable to cargo to be hoisted, means disposed on the free end of said boom detachably connectable to said carrier means, and means disposed on said helicopter and extending entirely within said boom for retracting said extensible boom along its length.
 2. A cargo hoist system for a helicopter according to claim 1, wherein said extensible boom coMprises a plurality of telescopic sections.
 3. A cargo hoist system for a helicopter according to claim 1, wherein said extensible boom comprises a plurality of telescopic sections and wherein successive sections are provided with engageable surfaces for preventing rotary displacement of successive sections about the longitudinal axis of said extensible boom.
 4. A cargo hoist system for a helicopter according to claim 1, wherein said extensible boom comprises a plurality of telescopic sections each having a noncircular cross-sectional configuration and means disposed at the opposite ends thereof for limiting the longitudinal displacement thereof relative to a successive telescopic section.
 5. A cargo hoist system for a helicopter according to claim 1, wherein the connection of said extensible boom to said helicopter is operative to permit pitch and roll motions of said extensible boom.
 6. A cargo hoist system for a helicopter according to claim 1, wherein said carrier means includes a collapsible hoop and said means disposed on the free end of said extensible boom comprises a hook device operatively engageable with said hoop for engaging and suspending said carrier means on the free end of said extensible boom.
 7. A cargo hoist system for a helicopter according to claim 1, wherein said means for retracting said extensible boom comprises a winch including a cable having the free end thereof secured to the free end of said extensible boom.
 8. A cargo hoist system for a helicopter according to claim 1, including means for pivoting said boom in the extended condition about a pitch axis.
 9. A cargo hoist system for a helicopter according to claim 1, wherein said means for retracting said extensible boom comprises a winch including a strap having the free end thereof secured to said means detachably connectable to said carrier means.
 10. A cargo hoist system for a helicopter according to claim 1, wherein said extensible boom comprises a plurality of telescopic sections each having a noncircular cross-sectional configuration and means disposed at the opposite ends thereof for limiting the longitudinal displacement thereof relative to a successive telescopic section and wherein said means for retracting said extensible boom comprises a winch disposed adjacent said helicopter including a multiple-ply lifting strap having the free end thereof secured to said means detachably connectable to said carrier means.
 11. A cargo hoist system for a helicopter according to claim 1, wherein said extensible boom comprises a plurality of telescopic sections each having a noncircular cross-sectional configuration and means disposed at the opposite ends thereof for limiting the longitudinal displacement thereof relative to a successive telescopic section, said connection of said extensible boom to said helicopter is operative to permit pitch and roll motions of said extensible boom, said carrier means includes a hoop, said means disposed on the free end of said extensible boom comprises a hook device mounted on a telescopic boom section, operatively engageable with said hoop for engaging and suspending said carrier means on the free end of said extensible boom, and said means for retracting said extensible boom comprises a winch disposed adjacent said helicopter including a multiple-ply lifting strap having the free end thereof secured to the telescopic boom section at the free end of said extensible boom, and including means for pivoting said extensible boom in the extended condition about its pitch axis.
 12. A cargo hoist system for a helicopter according to claim 1, wherein said means for retracting said extensible boom comprises a winch including a winding drum disposed adjacent the helicopter and a cable reeved about a first set of sheaves mounted on the free end of said extensible boom and a second set of sheaves mounted adjacent said drum, and the free end thereof secured to the free end of said extensible boom.
 13. A cargo hoist system according to claim 1, wHerein said carrier means detachably connectable to cargo to be hoisted, comprises an elongated frame adapted to be positioned on the cargo to be hoisted, a hoop adapted to be engaged and connected by said detachably connectable means disposed on the free end of said boom, and means for detachably securing said cargo to the underside of said frame.
 14. A cargo hoist system for a helicopter according to claim 13, wherein said means for securing said cargo to the underside of said elongated frame comprises a plurality of straps adapted to be passed under the cargo and drawn taut to positively secure the cargo to the underside of said elongated frame.
 15. A cargo hoist system for a helicopter according to claim 1, wherein said extensible boom comprises a plurality of telescopic sections each having a noncircular cross-sectional configuration and means disposed at the opposite ends thereof for limiting the longitudinal displacement thereof relative to a successive telescopic section, and wherein said connection of said extensible boom to said helicopter includes a mounting bracket mounted on said helicopter, a mounting frame pivotally connected to said mounting bracket and a base end telescopic section pivotally connected to said mounting frame.
 16. A cargo hoist system for a helicopter according to claim 13, wherein said pivotal connection between said mounting frame and said mounting bracket permits pivotal movement of said boom about a roll axis and said pivotal connection between the base and telescopic section of said boom and said mounting frame permits pivotal movement of said boom about a pitch axis.
 17. A cargo hoist system according to claim 16, including means for dampening any oscillating motion of said extensible boom about at least one of said axes.
 18. A cargo hoist system for a helicopter according to claim 15, wherein said means for retracting said extensible boom comprises a winch including a winding drum operatively mounted on said mounting frame and a cable extending through said telescopic boom sections and connected at its free end to the telescopic boom section at the free end of said boom, and means mounted on said mounting frame for operating said winch.
 19. A cargo hoist system according to claim 18, including a first set of sheaves mounted on said mounting frame and a second set of sheaves mounted on said telescopic boom section at the free end of said boom, and wherein said cable is reeved about said sheaves.
 20. A cargo hoist system according to claim 15, including a hydraulic cylinder assembly operatively interconnecting said helicopter and a base end telescopic section for pivoting said boom fore and aft about a pitch axis, and remote control means for operating said hydraulic cylinder assembly.
 21. A cargo hoist system for a helicopter according to claim 15, wherein said connection of said extensible boom to said helicopter permits pivotal movements of said boom about roll and pitch axes, and wherein said means for retracting said extensible boom comprises a winch including a winding drum rotatably mounted on said mounting frame, having an axis of rotation disposed parallel to said pitch axis, and a multiple ply lifting strap extending through said telescopic boom sections and connected at its free end to the telescopic boom sections at the free end of said boom, and means mounted on said mounting frame for operating said winch including remote control means.
 22. A cargo hoist system according to claim 17, including a first set of sheaves rotatably mounted on said mounting frame, having axes disposed parallel to the axis of rotation of said winding drum, and a second set of sheaves rotatably mounted on said telescopic boom section at the free end of said boom, and wherein said strap is reeved about said sheaves.
 23. A cargo hoist system according to claim 15, wherein said extensible boom comprises a plurality of telescopic sections each having a noncircular cross-sectional configuration and means disposed at thE opposite ends thereof for limiting the longitudinal displacement thereof relative to a successive telescopic section, and wherein said connection of said extensible boom to said helicopter includes a bracket mounted on said helicopter, a mounting frame pivotally connected to said mounting bracket to permit movement of said extensible boom about a roll axis, said mounting frame having a pair of downwardly extending arm sections, a base end telescopic section pivotally connected to the arm sections of said mounting frame to permit pivotal movement of said extensible boom about a pitch axis, and wherein said means for retracting said extensible boom comprises a winch including a winding drum rotatably connected to said frame member between said arm sections, having an axis of rotation disposed parallel with said pitch axis, and a multiple-ply lifting strap extending through said telescopic boom sections and connected at its free end to the telescopic boom section at the free end of said boom, and means mounted on said mounting frame for operating said winch having remote control means.
 24. A cargo hoist system according to claim 18, including a hydraulic cylinder assembly operatively interconnecting said helicopter and said base end telescopic section for pivoting said boom fore and aft about said pitch axis, and remote control means for operating said hydraulic cylinder assembly.
 25. A cargo hoist system according to claim 23, including a first set of sheaves rotatably mounted on said mounting frame between said arm sections, having the axes thereof disposed parallel to the axis of rotation of said winding drum, and a second set of sheaves mounted on said telescopic boom section at the free end of said boom, having the axes thereof disposed parallel to the axis of rotation of said winding drum, and wherein said strap is reeved about said sheaves.
 26. A cargo hoist system for a helicopter comprising a boom extensible along its length, operatively connected at one end thereof to said helicopter, carrier means detachably connectable to cargo to be hoisted, means disposed on the free end of said boom detachably connectable to said carrier means, and means for retracting said extensible boom, said extensible boom comprising a plurality of telescopic sections each having a noncircular cross-sectional configuration and means disposed at the opposite ends thereof for limiting the longitudinal displacement thereof relative to a successive telescopic section and said means for retracting said extensible boom comprising a winch disposed adjacent said helicopter including a multiple-ply lifting strap having free end thereof secured to said means detachably connectable to said carrier means.
 27. A cargo hoist system for a helicopter comprising a boom extensible along its length, operatively connected at one end thereof to said helicopter, carrier means detachably connectable to cargo to be hoisted, means disposed on the free end of said boom detachably connectable to said carrier means, means for retracting said extensible boom, aid extensible boom comprising a plurality of telescopic sections each having a noncircular cross-sectional configuration and means disposed at the opposite ends thereof for limiting the longitudinal displacement thereof relative to a successive telescopic section, said connection of said extensible boom to said helicopter being operative to permit pitch and roll motions of said extensible boom, said carrier means including a hoop, said means disposed on the free end of said extensible boom comprising a hook device mounted on a telescopic boom section, operatively engageable with said hoop for engaging and suspending said carrier means on the free end of said extensible boom, and said means for retracting said extensible boom comprising a winch disposed adjacent said helicopter including a multiple-ply lifting strap having the free end thereof secured to the telescopic boom section at the free end of said extensible boom, and means for pivoting said eXtensible boom in the extended condition about its pitch axis.
 28. A cargo hoist system for a helicopter comprising a boom extensible along its length, operatively connected at one end thereof to said helicopter, carrier means detachably connectable to cargo to be hoisted, means disposed on the free end of said boom detachably connectable to said carrier means, and means for retracting said extensible boom, said means for retracting said extensible boom comprising a winch including a winding drum disposed adjacent the helicopter and a cable reeved about a first set of sheaves mounted on the free end of said extensible boom and a second set of sheaves mounted adjacent said drum, and the free end thereof secured to the free end of said extensible boom.
 29. A cargo hoist system for a helicopter comprising a boom extensible along its length, operatively connected at one end thereof to said helicopter, carrier means detachably connectable to cargo to be hoisted, means disposed on the free end of said boom detachably connectable to said carrier means, and means for retracting said extensible boom, said extensible boom comprising a plurality of telescopic sections each having a noncircular cross-sectional configuration and means disposed at the opposite ends thereof for limiting the longitudinal displacement thereof relative to a successive telescopic section, said connection of said extensible boom to said helicopter boom sections and connected at its free end to the telescopic boom section at the free end of said boom, and means mounted on said mounting frame for operating said winch including remote control means.
 30. A cargo hoist system according to claim 29, including a first set of sheaves mounted on said mounting frame and a second set of sheaves mounted on said telescopic boom section at the free end of said boom, and wherein said cable is reeved about said sheaves.
 31. A cargo hoist system for a helicopter comprising a boom extensible along its length, operatively connected at one end thereof to said helicopter, carrier means detachably connectable to cargo to be hoisted, means disposed on the free end of said boom detachably connectable to said carrier means, and means for retracting said extensible boom, said extensible boom comprising a plurality of telescopic sections each having a noncircular cross-sectional configuration and means disposed at the opposite ends thereof for limiting the longitudinal displacement thereof relative to a successive telescopic section, said connection of said extensible boom to said helicopter including a mounting bracket mounted on said helicopter, a mounting frame pivotally connected to said mounting bracket and a base end telescopic section pivotally connected to said mounting frame, said connection of said extensible boom to said helicopter permits pivotal movements of said boom about roll and pitch axes, and said means for retracting said extensible boom comprising a winch including a winding drum rotatably mounted on said mounting frame, having a axis of rotation disposed parallel to said pitch axis, and a multiple ply lifting strap extending through said telescopic boom sections and connected at its free end to the telescopic boom section at the free end of said boom, and means mounted on said mounting frame for operating said winch including remote control means.
 32. A cargo hoist system according to claim 31, including a first set of sheaves rotatably mounted on said mounting frame, have axes disposed parallel to the axis of rotation of said winding drum, and a second set of sheaves rotatably mounted on said telescopic boom section at the free end of said boom, and wherein said strap is reeved about said sheaves.
 33. A cargo hoist system for a helicopter comprising a boom extensible along its length, operatively connected at one end thereof to said helicopter, carrier means detachably connectable to cargo to be hoisted, means disposed on the free end of said boom detachably connectable to said carrier means, and means fOr retracting said extensible boom, said extensible boom comprising a plurality of telescopic sections each having a noncircular cross-sectional configuration and means disposed at the opposite ends thereof for limiting the longitudinal displacement thereof relative to a successive telescopic section, said connection of said extensible boom to said helicopter includes a mounting bracket mounted on said helicopter and a mounting frame pivotally connected to said mounting bracket, said mounting frame having a pair of downwardly extending arm sections, a base end telescopic section pivotally connected to the arm sections of said mounting frame to permit pivotal movement of said extensible boom about a pitch axis, and said means for retracting said extensible boom comprising a winch including a winding drum rotatably connected to said frame member between said arm sections, having an axis of rotation disposed parallel with said pitch axis, and a multiple-ply lifting strap extending through said telescopic boom sections and connected at its free end to the telescopic boom section at the free end of said boom, and means mounted on said mounting frame for operating said winch having remote control means.
 34. A cargo hoist system according to claim 33, including a hydraulic cylinder assembly operatively interconnecting said helicopter and said base end telescopic section for pivoting said boom fore and aft said pitch axis, and remote control means for operating said hydraulic cylinder assembly.
 35. A cargo hoist system according to claim 33, including a first set of sheaves rotatably mounted on said mounting frame between said arm sections, having the axes thereof disposed parallel to the axis of rotation of said winding drum, and a second set of sheaves mounted on said telescopic boom section at the free end of said boom, having the axes thereof disposed parallel to the axis of rotation of said winding drum, and wherein said strap is reeved about said sheaves. 